Invasive species, including cats (Felis catus), rabbits (Oryctolagus cuniculus), goats (Capra hircus), rats (Rattus spp.), cane toads (Rhinella marina), foxes (Vulpes vulpes), feral pigs (Sus scofa), escaped or dumped domestic animals or pets, red imported fire ants (Solenopsis invicta) and yellow crazy ants (Anoplolepis gracilipes), are listed as the cause of decline in native species and/or ecological communities in 12 of the 21 key threatening processes listed under the EPBC Act.
Predation by cats and red foxes has contributed the most to extinction of mammals in Australia, and this pressure continues to contribute to the decline of threatened mammals (Woinarski et al. 2015). For example, a recent analysis of the diet of feral cats recorded 400 vertebrate species (native and non-native) that feral cats feed on or kill in Australia (Doherty et al. 2015). These included 17 EPBC Act–listed species, 123 birds, 157 reptiles, 58 marsupials, 27 rodents, 5 bats, 21 frogs, and 9 medium-sized and large exotic mammals. Cats also consume a wide range of insects, spiders, scorpions, centipedes and crustaceans.
Other significant animal invaders include cane toads and rabbits. Cane toads have been reported in the Kimberley and upper reaches of the Fitzroy River in Western Australia (Pusey & Kath 2014), and inland western Queensland, with estimates of expansion of their range of around 10–50 kilometres per year. Poisoning by cane toads is a major threat for 4 species of threatened mammals—for example, cane toads significantly affect populations of the northern quoll (Dasyurus hallucatus) in northern Australia.
In the past, the introduced black rat (Rattus rattus) has contributed to the extinction of several mammal species, as well as some island subpopulations, through predation, competition or disease transmission. Today, it is considered a major threat for a number of other threatened species in The action plan for Australian mammals 2012 (Woinarski et al. 2014a). Black rats have invaded bushland areas around most of Australia’s major coastal cities, often replacing native mammals that have become locally extinct.
Invasive animals that put pressure on inland waters include cane toads, common carp (Cyprinus carpio), eastern gambusia (Gambusia holbrooki) and goldfish (Carassius auratus). Approximately 43 invasive freshwater fish species have established wild populations, 34 of which continue to spread. This number is uncertain, because survey data are scarce and unevenly distributed across aquatic ecosystems.
The distribution of carp throughout inland waters in Australia is similar to that reported in 2011. Although the eastern gambusia is one of the more widespread invasive freshwater fish species in Australia, with sightings in all mainland states and territories, data from the Atlas of living Australia show no significant expansion in the species distribution since 2011.
Several introduced species are widespread in the marine environment, including the New Zealand screw shell (Maoricolpus roseus) (Gunasekera et al. 2005) and the northern Pacific starfish (Asterias amurensis) (Ross et al. 2003). These species were likely introduced through biofouling of ship hulls or ballast discharge.